# AP Annual Conference: Results from AP Physics Exams

Results from AP Exams

I attended this session to gain some insights into how the AP Physics B exam is scored and what common mistakes students made on the exam.

• Question B1
• 6.6/10
• common errors
• omit one of the three forces or add a normal force on FBD
• use unconventional labels for their forces
• units! students often omitted units
• not recognize buoyancy is measured in Newtons
• forces that appeared on the FBD often did not match the ones appeared in subsequent calculations
• not using physics but general language in justification
• Question B2
• 6.0/15
• common errors
• applied kinematic equations for constantly accelerated motion to a motion of changing acceleration
• not recognize that W=Fd can only be used when F is constant
• not knowing that spring force is not a constant force
• explanations are not concise and clear
• Question B3
• 3.6/10
• common errors
• non-linear scaling of axes in graphing
• best-fit line often is drawn by just connecting points
• not showing work for calculating slope of the best-fit line
• not understanding that the light must pass from a higher index of refraction to a lower index of refraction in order to have total internal reflection
• Question B4
• 3.6/10
• common errors
• not showing enough work beginning with the correct equations and then all the needed steps leading to an answer
• messing up the horizontal and the vertical dimensions in calculations
• deficiency in understanding the conservation of momentum
• using “energy,” “force,” “momentum” and “velocity” interchangeable in explanations
• Question B5
• 3.6/10
• common errors
• misunderstanding of the sign conventions in evolved for heat, work and energy
• not clear with their justifications, but often simply restated the question, and answer without providing further support
• connected heat or average kinetic energy to temperature, but not to the internal energy
• used W = -PΔV and did not discuss the effect of temperature on the pressure
• Question 6
• 3.5/15
• common errors
• simple calculations errors were everywhere
• incorrect use or value of the magnetic permeability, μo, in Ampere’s Law
• not understanding the intent of parts (a) & (b)
• did not clearly understand the nature of the question and the connection of the parts to each other
• Question 7
• 2.7/10
• common errors
• the most common errors were the result of a lack of understanding of atomic states and associated energy levels. Students seemed to choose and use the equations without basic understanding of the physics involved.

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